# Interpolation in usrp\_siggen **URL:** \ **Category:** GNU Radio\ **Created:** [December 12, 2006, 5:31am UTC](https://www.ruby-forum.com/t/interpolation-in-usrp-siggen/79107 "2006-12-12T05:31:15Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![Shyamnath](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/ecae2f/32.png) [@Shyamnath](https://www.ruby-forum.com/u/Shyamnath)\ **Post date:** [December 12, 2006, 5:31am UTC](https://www.ruby-forum.com/t/interpolation-in-usrp-siggen/79107/1 "2006-12-12T05:31:15Z")
hi, I am new to gnuradio architecture and am trying to learn about it. I was using the usrp\_siggen,py sample code provided with different interpolation rates (4, 8,12,16,64) since it has to be a multiple of 4. the observations are as follows (which cannot explain) 1. For interpolation rates set to 4,8,12, at the sender, what I observe on the receiver (directly connecting the usrp\_source to a file\_sink), is just noise. 2. For a interpolation rate set to 64, I almost get the required sinuosoidal at the required frequence(100khz), with the difference that the frequency of the signal at the receiver for nearly 200 samples at the beginning is nearly 7KHZs. To understand this better, I just send a constant signal on the sender (using usrp\_siggen.py) and received a sinousoidal at the receiver with a frequency of 7Khz (which I presume is because of the frequency offset). Although I think the above two observations are related I could not explain them. 3. Another interesting case is when the interpolation rate is set to 16. the output at the reciver is a signal which has a sinousoidal with the required frequency(100khz) spaced with sinousoidals with a frequency of 7khzs. This observation is something I cannot understand. Kindly help me out with this. ## Thanks Shyam View this message in context: [http://www.nabble.com/Interpolation-in-usrp\_siggen-tf2805450.html#a7827210](http://www.nabble.com/Interpolation-in-usrp_siggen-tf2805450.html#a7827210) Sent from the GnuRadio mailing list archive at [Nabble.com](http://Nabble.com). ---
**Author:** ![Shyamnath](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/ecae2f/32.png) [@Shyamnath](https://www.ruby-forum.com/u/Shyamnath)\ **Post date:** [December 12, 2006, 6:47am UTC](https://www.ruby-forum.com/t/interpolation-in-usrp-siggen/79107/2 "2006-12-12T06:47:25Z")
On Mon, Dec 11, 2006 at 08:30:25PM -0800, Shyamnath wrote: > output at the reciver is a signal which has a sinousoidal with the required > frequency(100khz) spaced with sinousoidals with a frequency of 7khzs. This > observation is something I cannot understand. > > Kindly help me out with this. > > Thanks > Shyam You didn’t mention which daughterboard you are using, but assuming it’s a Basic Tx, be sure to set the -f option to something like 10M. Neither the Basic Tx nor Basic Rx will pass signals under about 100kHz. Eric ---
**Author:** ![Shyamnath](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/ecae2f/32.png) [@Shyamnath](https://www.ruby-forum.com/u/Shyamnath)\ **Post date:** [December 12, 2006, 7:05am UTC](https://www.ruby-forum.com/t/interpolation-in-usrp-siggen/79107/3 "2006-12-12T07:05:26Z")
hi Eric, The daughterboard I use is RFX2400 so I set -f 2.45G ( btw my gnuradios have been properly set up since benchmark\_tx and receive work fine for gmsk) . I have tried the below stated experiment using two antenna types to see if it is due to the antennas but it is consistent across antennas. 2400-2480 MHz ISM Band PCB Quad Patch, and 2400-2480 MHz ISM Band Vertical Antenna. Also for the above configuration can u kindly also let me know is my observation that 7KHz is the frequency offset due to the oscillators is true? Thanks in advance for ur reply Shyam ---
**Author:** ![Shyamnath](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/ecae2f/32.png) [@Shyamnath](https://www.ruby-forum.com/u/Shyamnath)\ **Post date:** [December 12, 2006, 7:05pm UTC](https://www.ruby-forum.com/t/interpolation-in-usrp-siggen/79107/4 "2006-12-12T19:05:09Z")
On Tue, Dec 12, 2006 at 09:35:00AM -0800, John C. wrote: > Eric B. schrieb: > > > Are you seeing underruns (“uU”) on stderr? If so, then for your low > > interpolation rate cases your system is failing to be able to drive > > the USRP at full speed (32MB/s). What kind of h/w are you running? > > Speaking of which, what does ‘uO’ mean? > > Thanks > John C… uU = USRP underrun uO = USRP overrun aU = audio underrun aO = audio overun Eric ---
**Author:** ![Shyamnath](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/ecae2f/32.png) [@Shyamnath](https://www.ruby-forum.com/u/Shyamnath)\ **Post date:** [December 12, 2006, 5:48pm UTC](https://www.ruby-forum.com/t/interpolation-in-usrp-siggen/79107/5 "2006-12-12T17:48:49Z")
On Tue, Dec 12, 2006 at 01:03:08AM -0500, Shyam wrote: > Also for the above configuration can u kindly also let me know is my > observation that 7KHz is the frequency offset due to the oscillators is > true? > > Thanks in advance for ur reply > Shyam Are you seeing underruns (“uU”) on stderr? If so, then for your low interpolation rate cases your system is failing to be able to drive the USRP at full speed (32MB/s). What kind of h/w are you running? 7KHz offset between two 2.4GHz boards is well within spec. That’s only 3 parts per million. There’s a known problem with the first few samples being hosed on either or both of receive and transmit. Larry Doolittle fixed this in his UXO sweeper gadget, but we have yet to sort out the fix and integrate it into our USRP firmware. Eric ---
**Author:** ![Shyamnath](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/ecae2f/32.png) [@Shyamnath](https://www.ruby-forum.com/u/Shyamnath)\ **Post date:** [December 12, 2006, 6:35pm UTC](https://www.ruby-forum.com/t/interpolation-in-usrp-siggen/79107/6 "2006-12-12T18:35:00Z")
Eric B. schrieb: > Are you seeing underruns (“uU”) on stderr? If so, then for your low > interpolation rate cases your system is failing to be able to drive > the USRP at full speed (32MB/s). What kind of h/w are you running? Speaking of which, what does ‘uO’ mean? Thanks John C… ---
**Author:** ![Shyamnath](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/ecae2f/32.png) [@Shyamnath](https://www.ruby-forum.com/u/Shyamnath)\ **Post date:** [December 12, 2006, 7:59pm UTC](https://www.ruby-forum.com/t/interpolation-in-usrp-siggen/79107/7 "2006-12-12T19:59:49Z")
Hi Eric, The OS I am using is Linux 2.6.17-1.2174\_FC5 The hardware I am using is Memory of 512MB, Intel(R) Celeron(R) CPU 2.53GHz. As u predicted, I do observe a number of underruns on stderr when the interpolation rate is set to low values. This might explain the results for the case when interpolation is set to 16 but I dont understand still why the receiver is getting almost nothing when the interpolation at the sender is 4, 8,12. The decimation rate is set to constant at the receiver at 64. Your mail has raised a number of questions with me (kindly bear with me). 1. What is the behavior (output) of the DUC and interpolator when it doesnot get samples at the required rate (say it gets a burst of them with a period of silence followed by another burst)? 2. How do I bypass the bandpass filter on the RFX 2400, it would be great if I could move to some other frequency range which doesn’t have 802.11 interference. 3. What happens when I quit a program which is sending a sinosoidal using ctrl-c (like the usrp\_siggen.py). I mean what is the reaction of the usrp. I am asking this because of yet another observation, when I see the signal at the receiver in this case. The end of the samples for the sinusoidal I am observing again ends with a low frequency component and then a low amplitude component, I have attached the plots on the site. [http://nms.csail.mit.edu/~gshyam/sineStop2.jpg](http://nms.csail.mit.edu/~gshyam/sineStop2.jpg) The x axis is the samples and the y axis the I component of the signal. As u can see at the sampl point 4000 the low frequency sin(7.45k) starts. [http://nms.csail.mit.edu/~gshyam/sineStop1.jpg](http://nms.csail.mit.edu/~gshyam/sineStop1.jpg) This figure shows how the low frequency component ends. Kindly pls answer my questions. Thanks a ton for ur time Shyam